Method for operating a restraint system connected by a bus line in case of a short circuit

ABSTRACT

In the restraint system, a central control unit and a plurality of data processing units are coupled to a bus line, each of the data processing units being provided to activate one or more restraint devices. In order to keep the restraint system operational to the extent possible in the event of a short circuit, each data processing unit measures for short circuits on the bus line and starts timing if a short circuit is detected. Each data processing unit has a circuit breaker, with which the bus line can be closed or interrupted. This circuit breaker is opened if the short circuit measured is longer than a preset waiting time.

FIELD OF THE INVENTION

The present invention relates to a method for operating a restraintsystem, networked via a bus line, in the event of a short circuit on thebus line, including a central control unit and a plurality of dataprocessing units connected to the bus line, each of the data processingunits serving to activate one or more restraint devices.

BACKGROUND INFORMATION

The capabilities of vehicle restraint systems will increasesubstantially in the future in order to afford passengers still greaterprotection. This means that there will be a tremendous increase in thenumber of restraint devices and associated triggering means installed invehicles. Examples of such restraint devices are driver andfront-passenger airbags, which can be activated in multiple stages,driver and front-passenger knee bags, side airbags for the driver andthe front-seat and back-seat passengers, such side airbags optionallybeing provided for both the head and chest areas, seat-beltpretensioners, which also can be activated in multiple stages,optionally also roll bars, etc. A complex protection system composed ofmultiple restraint devices for each-passenger will thus be installed invehicles.

A complex restraint system is described in the German Patent ApplicationNo. 47 668.2 and in the Conference Proceedings of the SAE InternationalCongress and Exposition, Feb. 24-27, 1997, Detroit, in the paper“Bussystem zur Vernetzung von Aktuatoren für Rückhaltesysteme” [“BusSystem for Networking Actuators for Restraint Systems”] by J. Bauer, G.Mehler and W. Nitschke. Implementation of a bus system networking allthe restraint devices together made it possible to avoid the use ofbulky cable harnesses. In this conventional system, provided for eachrestraint device is a data processing unit, including a processor, datainput and output circuits, a memory unit, a time and clock base and apower supply. This data processing unit, also described as a peripheralintelligent driver stage, is located in the immediate vicinity of thetriggering device belonging to the respective restraint device, namely,in a firing-pellet connector or a substrate of the firing pellet itself.

Each data processing unit receives its power from a central controlunit, via a bus line. In addition, the central control unit determineswhich restraint devices are to be triggered, on the basis of a pluralityof control signals, for example, from acceleration sensors, pre-crashsensors and seat-occupancy sensors. Accordingly, with the aid of aprotocol transmitted over the bus line, the central control unitaddresses the data processing units concerned. In addition, requests fordiagnostic activity are transmitted from the central control unit viathe bus line to the individual data processing units, which in turn sendtheir diagnostic responses back to the central control unit via the bus.

As already described in German Patent Application No. 196 47 668.2,failure of the entire restraint system is to be prevented in the eventof a short circuit occurring on the bus line, if at all possible. Tothis end, the central control unit measures short-circuit current on thebus line, and localizes the short circuit by interacting with the dataprocessing units connected to the bus line. This makes it possible forat least all the data processing units located between the centralcontrol unit and the short circuit to remain operational, with onlythose data processing units downstream of the short circuit no longerbeing accessible to activation by the central control unit. The bussystem constructed in this way thus has a certain tolerance for shortcircuits.

SUMMARY OF THE INVENTION

An object of the present invention is to specify a device of the which,as far as possible, maintains the entire restraint system operational inthe event of a short circuit on the bus line.

The objective is achieved in that data processing unit in that each dataprocessing unit connected to the bus line measures for short circuits onthe bus line. If a short circuit is detected, the data processing unitthen starts timing, and opens a circuit breaker contained within it,with which the bus line can be closed or interrupted, if the shortcircuit measured lasts longer than a preset waiting period.

As all the data processing units used to activate various restraintdevices are themselves actively involved in detecting a short circuit,an optimum short-circuit tolerance in the restraint system can beachieved. Namely, the duration of the short circuit is taken intoaccount, such that in the event of a short circuit of only briefduration, the entire restraint system is maintained in an operationalstate, and in the event of a longer short circuit, at least those dataprocessing units located between the central control unit and thelocalized short circuit remain active. As a result, a short circuit onthe bus line does not inevitably lead to a total failure of the entirerestraint system.

The data processing unit can be shifted into a reset state if theduration of the short circuit measured is several times longer than thewaiting period after which the circuit breaker is opened.

In practical terms, the central control unit performs a short-circuitmeasurement on the bus line, starts a time measurement with thecommencement of a short circuit, and switches off its power supply tothe data processing units connected to the bus line if the short-circuitduration measured by it exceeds a preset hold time. This hold time isshorter than the delay for the opening of the circuit breakers in thedata processing units. The central control unit switches the powersupply for the data processing units back on again after the latter haveopened their circuit breakers. As a result, operation of those dataprocessing units which are disposed between the central control unit andthe location of the short circuit can be maintained.

When a triggering command for the restraint devices has to betransmitted after the onset of a short circuit, the central control unittransmits it several times via the bus line, such that after a shortcircuit of very brief duration, a triggering command will be guaranteedto reach all data processing units concerned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a restraint system according to thepresent invention.

FIG. 2 shows a block diagram of a data processing unit according to thepresent invention.

FIG. 3 shows a flow diagram illustrating a method according to thepresent invention.

DETAILED DESCRIPTION

FIG. 1 shows a section of a restraint system, including a centralcontrol unit ZS, a bus line BL connected to it and a plurality of dataprocessing units DV1, DV2 coupled to bus line BL. Bus line BL isembodied here as a stub line, but it can equally well be in the form ofa ring circuit. Central control unit ZS, in addition to a logic orsignal processing device not shown here, also includes a bus interfaceBS. This bus interface BS includes a circuit breaker S, ameasured-current source MS, a current-measuring device SM and signaldrivers, which, however, are not shown here because they are notrelevant to the present invention. Central control unit ZS can beconnected to or disconnected from bus line BL by way of circuit breakerS; in other words, power-supply and/or control signals can be passedthrough from central control unit ZS to data processing units DV1, DV2,or their transmission can be interrupted, via circuit breaker S.

All of data processing units DV1, DV2, two of which are shown asexamples, have the same circuit pattern as illustrated in FIG. 2, andwill be explained in detail below. Each of data processing units DV1,DV2 provided is used to activate one or more restraint devices RH1, . .. RHk. These restraint devices include, for example, airbags for thedriver and the front passenger, which can be activated in multiplestages; driver and front-passenger knee bags; side airbags for thedriver, the front passenger and the rear passengers; seat-beltpretensioners, etc. In addition to the connections to the bus line, dataprocessing devices DV1, DV2 also have additional inputs e1, . . . en,for example, for signals from acceleration sensors and/or pre-crashsensors and/or seat occupancy sensors. These data processing units DV1,DV2 are thus able to activate one or more restraint devices RH1, . . .RHk autonomously and independently of control signals from centralcontrol unit ZS.

FIG. 2 shows the circuit structure of a data processing unit DV. Thegroup of k restraint devices RH1 to RHk connected to this dataprocessing unit DV may be assigned to one vehicle occupant, for example.If this is the front passenger, for example, then restraint devices RH1to RHk could include a front airbag, one or two side airbags in the headand chest areas, a knee airbag and a seat-belt pretensioner, with thepossibility of triggering all air bags and the seat-belt pretensioner inmultiple stages.

In the event of a crash, data processing unit DV generates a triggeringsignal a1 to ak for restraint devices RH1, . . . RHk; the restraintdevices to be triggered and the triggering times may be selected as afunction of a plurality of input signals e1 to en. Input signals e1 toen come from sensors, which may include one or more acceleration sensorsfor sensing the kinetic behavior of the vehicle in a crash, pre-crashsensors, a seatbelt-buckle sensor and seat-occupancy sensors. On thebasis of the signals from the seat-occupancy sensors, data processingunit DV concludes whether the front-passenger seat is occupied at all,whether a child or adult is sitting in it, and also in what position thepassenger is sitting, so that only those restraint devices will betriggered accordingly which are in fact able to offer protection, ratherthan perhaps even harming the person. In the same way, the triggering ofrestraint devices is completely suppressed if the front-passenger seatis not even occupied or if a child seat or an item of luggage is on it.

FIG. 2 illustrates the individual functional elements within dataprocessing unit DV, in the form of blocks. There is a signal inputcircuit 1 to receive analog or digital input signals e1 to en,containing signal drivers, for example, and possibly also a multiplexerfor the conversion of input signals received in parallel into a serialdata stream. In adjacent data preparation circuit 2, analog inputsignals may be subjected to an analog-digital conversion; in any event,at this stage the data are prepared in such a way that they can bedigitally further processed by a downstream processor 3.

Processor 3 carries out all control functions in data processing unitDV. For example, it determines on the basis of input signals e1 to enwhich of the connected restraint devices RH1 to RHk should be triggeredat what times. It also performs diagnostics on the firing components inrestraint devices RH1 to RHk. To that end, diagnostic signals d1 todk—for example, the resistance values of the firing components—aresupplied to signal input circuit 1. Processor 3 compares diagnosticsignals d1 to dk to reference values and outputs an error message in theevent of unacceptable deviations. Additionally, diagnostics areperformed on an energy reserve located in a power supply unit 4.

A memory unit 5 is used to store temporary data, such as resistances ofthe firing components, the power levels of the energy reserve, etc.Similarly, production-specific data and identification data can bestored in memory unit 5. Processor 3 can access the data in memory unit5 and can write new data to the memory unit 5.

In a similar arrangement to the input side of data processing unit DV,there is on the output side downstream of processor 3 a data preparationcircuit 6 and a signal output circuit 7. In data preparation circuit 6,for example, the digital triggering information or diagnostic scansignals from process or 3 are converted into firing currents or testcurrents for the firing components of restraint devices RH1 to RHk.Signal output circuit 7 is equipped with signal drivers and may also beequipped with a demultiplexer, which splits up a serial flow of outputsignal data into individual parallel output signals a1 to ak.

A time and clock base 8 in data processing unit DV supplies allfunctional blocks with a uniform and synchronous clock pulse.

It is evident that the arrangement of the functional blocks shown inFIG. 1 is not mandatory, but merely illustrative. For example, signalinput circuit 1 and data preparation circuit 2, or signal output circuit6 an d data preparation circuit 7, could be combined and could also beat least partially integrated into processor 3. Similarly, power supply4 and/or time and clock base 8 can be integrated into data preparationcircuits 2, 6. There are many different possibilities of incorporatingmultiple functions into one circuit block.

However, for the functions of the present invention described in moredetail below, it is not a requirement that the data processing units beautonomous systems in accordance with the preceding description.Decisions on the triggering of restraint devices m ay also b e made bycentral control unit ZS alone and communicated to the individual dataprocessing units via bus line BL. Similarly, the diagnostics onrestraint devices RH1, . . . RHk and data processing units DV1, DV2 canbe implemented from central control unit ZS.

As illustrated in FIG. 2, data processing unit DV is equipped with acircuit breaker 9, which makes it possible to isolate bus BL and/or toconnect it to the nearest data processing unit. The opening and closingof circuit breaker 9 is controlled by processor 3. A request to close oropen circuit breaker 9 can be transmitted from central control unit ZSvia bus line BL. This then makes it possible to activate individual dataprocessing units as specifically required, and to supply them withinformation, control signals and power signals. The grounding line ofbus BL, which here is in the form of a two-wire line, is contacted to acommon ground connection 10 in data processing unit DV. The other lineof bus BL is used to deliver the information and control signalstransmitted from central control unit ZS to signal input circuit 1 andthe power-supply signals to power supply unit 4.

Data processing unit DV incorporates a comparator 11, which taps voltageUb on bus BL and compares it to a reference voltage Ur. This comparisonmakes it possible to determine whether bus voltage Ub has collapsed as aresult of a short circuit on bus line BL.

It will now be described on the basis of the flow diagram in FIG. 3 howdata processing units DV and central control unit ZS act in the event ofa short circuit, in order to keep the entire restraint systemoperational to the extent possible. As indicated in blocks 12 and 13,both central control unit ZS and all of data processing units DV measurefor short circuits on bus line BL. As described above, the measurementwithin data processing units DV is carried out using a voltagecomparator 11. Central control unit ZS has a measured-current source MSand a current-measuring device SM for the short-circuit measurement inits bus interface BS. As soon as a short circuit occurs on bus line BL,current-measuring device SM detects a change in the current fed to thebus line from measured-current source MS.

As shown in blocks 14 and 15, both the central control unit and the dataprocessing units measure the duration of the short circuit. Both centralcontrol unit ZS and data processing units DV begin timing as soon as theoccurrence of a short circuit on the bus line is detected. If centralcontrol unit ZS, as shown in block 16, measures a duration for the shortcircuit which is longer than a time t1, it opens its circuit breaker S.This hold time t1 amounts, for example, to 100 microseconds. Whencircuit breaker S in central control unit ZS is open, data processingunits DV are isolated from the power supply in central control unit ZS.At that point, data processing units DV draw their power from thereserve in their power supply unit 4. If the short circuit comes to anend within a time which is shorter than hold time t1, then the entirerestraint system is unaffected. This is because central control unit ZSsends triggering commands repeatedly one after the other, so that one ofthe multiple triggering commands transmitted is guaranteed to reach therelevant data processing units DV after the short circuit.

As shown in block 17 of the flow diagram, data processing units DV alsoopen their circuit breakers 9 if they measure a short circuit which islonger than a time t2. This waiting time t2 is about one millisecond.Times t1 and t2 for the opening of the circuit breakers are made sodifferent in order to avoid interplay between the switching processes incentral control unit ZS and in data processing units DV, therebyavoiding oscillation throughout the entire bus system. The stipulationof the two times t1 and t2 is based on the shortest triggering-reactiontime in the restraint system, with the primary deciding factor being thevery short triggering time for side airbags.

The opening of circuit breakers 9 in data processing units DV has theeffect that the short circuit for central control unit ZS is canceled.As, if at a location upstream of the short circuit, the bus line hasbeen interrupted by one or more circuit breakers 9 in data processingunits DV, central control unit ZS will no longer detect a short circuit.At that point, central control unit ZS will then close its circuitbreaker S once again, as shown in block 18, and current can then besupplied at least to those data processing units DV which are locatedbetween central control unit ZS and the location of the short circuit.Consequently, the restraint system is at least partially stilloperational.

If, however, the duration of the short circuit measured in dataprocessing units DV is longer than a preset time t3, the energy reservein data processing units DV will be consumed and all data processingunits DV will carry out a reset, as indicated in block 19. Time t3 isshorter than one second.

What is claimed is:
 1. A method for operating a restraint system,networked via a bus line, in an event of a short circuit on the busline, comprising the steps of: coupling a central control unit and aplurality of data processing units to the bus line, each data processingunit being adapted to activate at least one restraint device; measuring,by each data processing unit, for a short circuit on the bus line;beginning a timing, by a particular data processing unit, when the shortcircuit is detected; and opening a circuit breaker, located inside theparticular data processing unit if the measured short circuit has a timeduration that is longer than a preset waiting time, the circuit breakerat least one of closing and interrupting the bus line.
 2. A method foroperating a restraint system, networked via a bus line, in an event of ashort circuit on the bus line, comprising the steps of: coupling acentral control unit and a plurality of data processing units to the busline, each data processing unit being adapted to activate at least onerestraint device; measuring, by each data processing unit, for a shortcircuit on the bus line; beginning a timing, by a particular dataprocessing unit, when the short circuit is detected; opening a circuitbreaker, located inside the particular data processing unit if themeasured short circuit has a time duration that is longer than a presetwaiting time, the circuit breaker at least one of closing andinterrupting the bus line; and shifting the particular data processingunit into a reset state if the measured short circuit has a timeduration that is several times longer than the preset waiting time afterwhich the circuit breaker is opened.
 3. A method for operating arestraint system, networked via a bus line, in an event of a shortcircuit on the bus line, comprising the steps of: coupling a centralcontrol unit and a plurality of data processing units to the bus line,each data processing unit being adapted to activate at least onerestraint device; measuring, by each data processing unit, for a shortcircuit on the bus line; beginning a timing, by a particular dataprocessing unit, when the short circuit is detected; opening a circuitbreaker, located inside the particular data processing unit if themeasured short circuit has a time duration that is longer than a presetwaiting time, the circuit breaker at least one of closing andinterrupting the bus line; measuring, by the central control unit, forthe short circuit on the bus line; beginning a timing, by the centralcontrol unit, when the short circuit occurs; switching off a powersupply to the plurality of data processing units, coupled to the busline, if the time duration of the measured short circuit, by the centralcontrol unit, exceeds a preset hold time, the preset hold time beingshorter than the preset waiting time; and switching on the power supplyto the plurality of data processing units, coupled to the bus line,after the plurality of data processing units have opened their circuitbreakers.
 4. A method for operating a restraint system, networked via abus line, in an event of a short circuit on the bus line, comprising thesteps of: coupling a central control unit and a plurality of dataprocessing units to the bus line, each data processing unit beingadapted to activate at least one restraint device; measuring, by eachdata processing unit, for a short circuit on the bus line; beginning atiming, by a particular data processing unit, when the short circuit isdetected; opening a circuit breaker, located inside the particular dataprocessing unit if the measured short circuit has a time duration thatis longer than a preset waiting time, the circuit breaker at least oneof closing and interrupting the bus line; and transmitting repeatedly,by the central control unit, over the bus line any triggering signal forthe at least one restraint device that has to be transmitted after theshort circuit occurs.